1. Field of the Invention
This invention relates generally to assemblies comprising indicia carrying concentric rotating discs and more particularly to an assembly for use as a slide rule, game, display device, reference guide or the like as well as a method of fabrication.
2. Background Disclosure
Assemblies of indicia bearing concentric rotating discs have been traced to the early seventeenth century and the development of analog calculating deices. Until the advent of electronic calculators, the logarithmic slide rule was a widely used, virtually essential, tool in mathematical science and engineering. Slide rules were used to rapidly perform calculations in such fields despite their somewhat limited accuracy.
The origins of the slide rule developed in 1620 from the recognition by Edmund Gunter, an English mathematician, that by plotting logarithms on a line, addition and subtraction of lengths by a pair of dividers would result in multiplication and division calculations. Another English mathematician, William Oughtred constructed a pair of Gunter's lines on concentric circular discs. Gunter's dividers were replaced by an opening index in one of the discs. Oughtred also fashioned two Gunter's scales in straight form with the scales held against one another and thus invented the precursor of linear slide rules.
Linear, rather than circular, slide rules became popular with the modern linear slide rule based upon an 1859 design of Amedee Mannheim. The prevalence of linear slide rules was due, in part, to the fact that circular slide rules were more difficult to manufacture. The increased manufacturing difficulty was attributed to the cutting and assembly of discs as well as inscribing circular scales.
The basic mode of construction of circular slide rules was incorporated throughout the years in various applications without imprinted logarithmic scales For example, the use of concentric circular discs has been employed in computing and calculating devices such as air navigation computers as illustrated in U.S. Pat. No. 2,423,764, nautical data corrolators as illustrated in U.S. Pat. No. 3,249,085, duplicate bridge scoring devices as shown in U.S. Pat. No. 3,280,788, and in animated display devices as illustrated in U.S. Pat. No. 2,492,906 and games as illustrated in U.S. Pat. Nos. 1,714,839 and 2,435,885.
These concentric rotating disc devices generally included at least three layers of discs with at least one of the discs being rotatable relative to the others and with openings provided in one of the discs for viewing only a selected portion of the indicia carried on another disc.
Manufacture of concentric rotating disc assemblies, such as those illustrated in U.S. Pat. Nos. 2,423,764, 3,249,085 and 3,280,788, generally included imprinting indicia on one or both faces of at least three separate discs with the discs having a die cut circular periphery, a central aperture and one or more window cursors. The printed discs were then assembled and an axle in the form of a solid rivet or an eyelet was inserted through the central aperture in each of the discs to secure the discs together while permitting relative rotation between the discs.
Among the problems which were encountered in manufacturing were the possibility of unskilled laborers inadvertently assembling the discs in an improper order or assembling the discs with a printed face oriented in an improper direction. Improper assembly destroyed the utility of the device.
U.S. Pat. No. 2,492,906 to VOGES and U.S. Pat. No. 2,435,885 to GERWITZMAN both disclosed a concentric rotating disc assembly which include an inner disc positioned between a front and back outer disc. The front and back outer discs were formed of a single sheet of folded paperboard. While this arrangement assured proper orientation of the outer discs, assembly of the completed device still required positioning the inner disc with its printed indicia facing in the correct directions. In addition, assembly of the device also entailed proper alignment of the central apertures of the outer discs and the inner disc and the subsequent insertion of an axle pivot and was susceptible to misalignment.
While concentric rotating disc assemblies would naturally have lended themselves to distribution as promotional or premium items due to their apparently simple construction of relatively inexpensive materials such as paperboard, because of the factors which inhibited low cost mass production and assembly, concentric rotating disc devices have been relatively costly and have not gained widespread acceptance.